Research will be continued, the aim of which is to explore the nature of the action of steroid hormones in the brain of infantile rats, which results in permanent changes in sex differentiation of the brain. Past efforts to show whether or not a regionally limited permanent alteration in genetic transcription occurs have yielded equivocal results for technical reasons. Further work involves improvement of the sensitivity and specificity of the DNA:RNA hybridization technique, and use of messenger-rich (poly-A) fractions of RNA. An in vitro perifusion technique for testing sex differentiated function of the hypothalamus has been developed and this will be used for further rapid assessment of experimentally induced functional changes. The undersigned agrees to accept responsibility for the scientific and technical conduct of the project and for provision of required progress reports if a grant is awarded as the result of this application. BIBLIOGRAPHIC REFERENCES: Yu, John Y.L., 1975. Regional and sexual distribution patterns of soluble cytoplasmic proteins in the rat brain. Jour. Neurochem., 24:1111-1116. Farquhar, M.N. and A. Gorbman, 1975. Testosterone uptake in neonatal rat brain tissue. Am. Zool., 15:815 (Abstract).